Generic Routing Encapsulation over CLNS Networks (RFC3147)
Original Publication Date: 2001-Jul-01
Included in the Prior Art Database: 2019-Feb-13
Internet Society Requests For Comment (RFCs)
This document proposes a method for transporting an arbitrary protocol over a CLNS (Connectionless Network Service) network using GRE (Generic Routing Encapsulation). This may then be used as a method to tunnel IPv4 or IPv6 over CLNS. This memo provides information for the Internet community.
Network Working Group P. Christian Request for Comments: 3147 Nortel Networks Category: Informational July 2001
Generic Routing Encapsulation over CLNS Networks
Status of this Memo
This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document proposes a method for transporting an arbitrary protocol over a CLNS (Connectionless Network Service) network using GRE (Generic Routing Encapsulation). This may then be used as a method to tunnel IPv4 or IPv6 over CLNS.
RFC 2784 Generic Routing Encapsulation (GRE)  provides a standard method for transporting one arbitrary network layer protocol over another arbitrary network layer protocol.
RFC 1702 Generic Routing Encapsulation over IPv4 networks  provides a standard method for transporting an arbitrary network layer protocol over IPv4 using GRE.
However no standard method exists for transporting other network layer protocols over CLNS. This causes lack of interoperability between different vendors’ products as they provide solutions to migrate from CLNS networks to IP networks. This is a problem specifically in, but not limited to, the context of management networks for SONET and SDH networks elements.
Large networks exist for the purpose of providing management communications for SONET and SDH network elements. Standards Bellcore GR-253-CORE  and ITU-T G.784  mandate that these networks are based on CLNS.
Christian Informational [Page 1]
RFC 3147 Generic Routing Encapsulation over CLNS Networks July 2001
Many vendors have already started to offer SONET and SDH products that are managed by IP instead of CLNS and a general migration from CLNS towards IP is anticipated within the industry.
Part of any migration strategy from CLNS to IP should provide for the co-existence of both CLNS managed and IP managed network elements in the same network.
Such a migration strategy should foresee the need to manage existing CLNS managed network elements that become isolated by a new IP network. Such a scenario may be tackled by tunnelling CLNP PDUs over IP using the existing GRE standard RFC 2784  and informational RFC 1702 . Networks have already been deployed that use this method.
Such a migration strategy should also foresee the need to manage new IP managed network elements that are installed on the far side of existing CLNS managed network. Such a scenario requires a method for tunnelling IP over CLNS.
2. GRE over CLNS advantages
Using GRE to tunnel IP over CLNS offers some advantages.
In the absence of a standard for tunnelling IP over CLNS, GRE as specified in RFC 2784  is the most applicable standard that exists.
The move from CLNS to IP comes at a time when IP is itself migrating from IPv4 to IPv6. GRE defines a method to tunnel any protocol that has an Ethernet Protocol Type. Th...